1. Field of the Invention
The present invention relates to a driving device, a lens barrel, and an optical apparatus including the lens barrel. More particularly, the present invention relates to a technique for relatively moving a vibrator and a contact member.
2. Description of the Related Art
In the field of vibration actuators, the so-called linear ultrasonic motor, i.e., a vibration actuator producing a linear motion, has been developed. The linear ultrasonic motor is featured in providing a relatively large output for the size of the vibrator, and in having good controllability. Such a vibration actuator producing a linear motion is used for driving a lens unit that is disposed in a lens barrel of a camera, for example.
Regarding that type of vibration actuator, Japanese Patent Laid-Open No. 2007-312519 proposes a mechanism for pressing a vibrator and a contact member as a driven member, the contact member being held in contact with the vibrator. More specifically, Japanese Patent Laid-Open No. 2007-312519 discloses a method of contacting the vibrator and the contact member with each other under pressure by utilizing a magnetic force of a permanent magnet. Also, Japanese Patent Laid-Open No. 2007-312519 discloses a structure that the permanent magnet is disposed on the vibrator side. In the disclosed structure, the permanent magnet is held by a holding member disposed between the vibrator and the contact member. Further, the vibrator is brought into pressure contact with the contact member by a magnetic attraction force. According to Japanese Patent Laid-Open No. 2007-312519, a small-sized vibration actuator having good spatial efficiency is realized by arranging the permanent magnet in a space that is formed between the vibrator and the contact member.
U.S. Patent Application Publication 2007/069609A1 proposes a structure that a permanent magnet is disposed on the contact member side. Further, U.S. Patent Application Publication 2007/069609A1 discloses a contact member including a slider base having a square bar shape and made of a magnet material, and a friction member disposed on a surface of the slider base on the side contacting with the vibrator.
However, when the permanent magnet is arranged in the space formed between the vibrator and the contact member as disclosed in Japanese Patent Laid-Open No. 2007-312519, the size of the permanent magnet is restricted by the size of the space, and a sufficient pressing force is not obtained in some cases. Further, when the contact member is fixed to a mirror barrel portion and the vibrator is moved, response of the vibrator may degrade due to the weight of the permanent magnet if the permanent magnet is arranged on the vibrator side.
When the permanent magnet is arranged on the contact member side as disclosed in U.S. Patent Application Publication 2007/069609A1, the permanent magnet is required to have a length longer than that of a driving range and the cost is increased in proportion to the length of the driving range.